ELECTRIC: OV-10 BRONCO

Model Airplane News, Jan 2006 by Sparks, Keith

A twin warbird that flies as good as it looks

The OV-10 Bronco makes an excellent first-time project: its trainer-type wing and boxy fuselage make construction fast and relatively easy. Add electric motors, and you have a dependable, multi-engine warbird that's fun to fly. Most RC Broncos that I've seen fly a little too fast for my taste; I wanted a model with close to scale speeds. The result is a 4-foot-span model with a flying weight of just a few ounces over 3 pounds. No flaps needed here!

My design has the advantage of modular construction. The five components that make up the model are relatively small, so you don't need a lot of space to build and transport the plane. Another plus is that, in the event of a crash, you need only repair or replace the damaged component. The disadvantage is the assembly time needed at the field, so when I transport my Bronco, 1 only separate the fuselage from the wing.

BUILDING THE WING

You will notice that I drew the plans in halves. I did this so you can work on both sides of the worktable at the same time. If you work on a narrow bench, you can fold the plans in half to save space.

You'll need the wing to test-fit the other components, so the construction begins there. The wing goes together like a slightly complex trainer wing, so everything is straightforward. Start by marking the spar and rib locations on the bottom sheeting and placing them on the plans. Glue the spar and the ribs into place; then glue the trailing-edge spar to the ribs and the bottom sheeting, and add the upper spar to lock the ribs in place. Pin the aileron leading edge to the aft spar. Use cellophane tape along the rear of the aft spar to prevent it from bonding to the aileron leading edge during assembly.

After you've installed the aileron ribs, use ¼-inch-square stock scrap as an alignment/spacer tool to install the dowel-support ribs R-3. After you've bonded the shear webbing, add the spar cross-braces. Making patterns for the braces will speed things up.

With weights placed across the top spar, pull the bottom sheeting up to meet the ribs at the front. Sliding sticks under the sheeting makes the task easier and prevents the sheeting from warping while the bond cures.

Use a servo with a scrap piece of 1/16-inch-thick balsa sheet under it to position the servo-mounting plate. Add the bolt-support plates, and you are ready to sand the wing for sheeting.

Use a long sanding bar to remove the high spots on top of the wing ribs and to taper the bottom sheeting at the trailing edge. Cut the gap between the aileron inboard end and the wing before you sheet the top. You should also cut the slot for the aileron control horn.

After you've installed the sheet and capstrips, sand the leading edge to prepare it for the leading-edge stock. Be sure to mark the locations between the R-3 ribs on the sheeting before the leading-edge stock is glued into place.

Use the aileron "gap cut" as a guide to cut the upper sheeting; then use a razor to cut the ailerons free of the wing. Bevel the aileron leading edge, and hinge and reinstall the ailerons. Glue the wingtips into place, and sand them to match the wing contour.

TAIL-BOOM ASSEMBLY

To ensure that the tail booms are identical, cut these parts while they're stacked together and assemble them at the same time. Start assembly by bonding the tri-stock into place along the edges of the tail-boom skins. You will have to make relief cuts so the tri-stock can bend at the lower forward end of the skins. Glue the skin doubters and stiffeners into place; add the 3/16-inch shim at the tail.

Mark the positions for the formers on the inside, and install the firewall tri-stock. Make sure that they are flush with the front edge of the skin. Before you install the formers, draw a centerline on both sides for alignment purposes.

Glue former B-3 into position on the right skin half: make sure that it's 90 degrees to the skin surface. Repeat the step with the left half.

Glue former B-2 into position using the marks you made earlier. Do this with the bottom of the boom on a flat surface.

Draw a straight line on the work surface as a centerline reference. Align the centerline marks on B-2 and B-3 to this line. Glue B1 into position h2 inch below the bottom edge of the booms to allow for the sheeting, and center it to the reference line. Sand away enough tri-stock at the tail to allow the shims to touch. With the boom centered over the reference line, bring the tailpieces together over the line and glue them.

Install the wing-attachment plates and supporting structure, and place the wing in the boom wing saddles. Align the dowel marks on the wing with the boom centerline, and drill a ¼-inch-diameter hole through the firewall (B-1) and the wing leading edge. Install the dowels in the wing, and test the fit before the adhesive sets.

With the booms installed on the wing, align the booms so their centerlines are parallel; then drill the pilot holes for the wing-attachment screws. Cut the threads for the nylon screws in the attachment plates, and install the screws.